How to get rid of triangulation in STL glass
The STL from a cad program is not going to have good topology. Topology is important for smooth shading and even more so for a glass shader.

It is kind of hard to tell from that one picture, but your mesh may have more issues then just bad topology.

A quick and easy way to possibly fix your mesh is to add a Remesh modifier.


That modifier will make a completely new mesh (out of evenly sized quads) that closely matches the shape of the original.